THE CRYSTAL-STRUCTURE OF INDOSPICINE HYDROCHLORIDE HYDRATE

The crystal structure of the hepatotoxic amino acid indospicine [L-6-amidino-2-aminohexanoic acid, (S)-2,7-diamino-7-iminoheptanoic acid], as its hydrochloride hydrate, has been determined by X-ray diffraction and refined to a residual R 0.036 for 845 observed reflections collected at 173 K. Crystals are orthorhombic, space group P 22(1)2(1) with 8 molecules in a cell of dimensions a 5.1541(4), b 14.083(1), c 31.781(3) angstrom. The structure is consistent with the one previously derived from chemical data but with the presence of a terminal amidinium ion and an alpha-amino acid zwitterion pair. The two independent molecules in the asymmetric unit are conformationally different and form a head-to-tail packing motif linked by NH(amidino)...O(carboxyl) hydrogen bonds (N...O, 2.80, 2.85 angstrom). The structure also features extensive hydrogen bonding involving the water of solvation.